In general this invention relates to sample spinning apparatuses for use in magnetic resonance spectroscopy systems, more particularly, it relates to apparatuses for holding samples which are spun in order to produce the sample's spectrum using nuclear magnetic resonance (NMR).
NMR (or, simply, Magnetic Resonance) spectroscopy is a non-destructive technique used to produce the spectrum of a liquid, solid, or gas sample so that the sample's structure or composition can be identified. This sample-identification technique is based upon the known fact that when substances containing nuclear spins are subjected to both a static magnetic field and an alternating electromagnetic field at a certain frequency and orientation, the substances emit radiation which is characteristic of the substances' molecular and atomic structure. Samples are placed within the strong magnetic field (typically 1-10 Tesla) produced by a large main, outer magnet as well as the field produced by a radio-frequency (RF) coil. If solid samples are not rotated at high speeds (typically 30,000-1,500,000 rpm) while positioned within the fields, the information available from the samples' spectrum is limited. Since the discovery of this fact, NMR spectroscopy is mainly performed on spinning samples. The requirement that samples be spun has created problems for the designers of NMR spectroscopy equipment.
Various sample spinning techniques exist to date. Magic Angle Spinning (MAS) is one spinning technique wherein the sample is rotated about its axis at an angle approximately 54.7 degrees (called the "magic angle") from the direction of the external static magnetic field generated by a large outer magnet. U.S. Pat. No. 4,940,942 issued to Bartuska et al. describes a MAS spin mechanism for use in Variable Temperature (VT) NMR spectroscopy. VT NMR spectroscopy is the technique used to produce the spectrum of a sample spun at a temperature other than the temperature at which the NMR equipment is operating. U.S. Pat. No. 4,899,111 issued to Pines et al. describes: (1) a technique often referred to as Double Rotation (DOR) wherein a sample or inner sample holder is rotated about its axis, while at the same time being spun in a "central cylinder" to allow the sample to precess; and (2) in column 11 of that patent, a technique often referred to as Dynamic Angle Spinning (DAS) wherein a sample or sample holder is rotated about its axis, while at the same time being pivoted. Doty Scientific, Inc. manufactures NMR spectrometer spinning mechanisms which operate using the DAS technique.
U.S. Pat. No. 4,968,939 issued to Pines et al. illustrates in FIG. 5 an apparatus that mechanically varies the orientation of a sample for measuring the sample's NMR spectra.
None of the known sample spinning devices used for obtaining the magnetic resonance spectra of samples are designed with mechanical bearings for allowing samples to freely spin with greater stability. All known NMR spectroscopy sample spinning devices (including those used for DOR, DAS, and MAS) use air/gas bearings for low-friction, high speed spinning of sample holders and outer housings. Air/gas bearings used in this manner cannot adequately support spinning samples, sample holders, or outer housings under all desirable circumstances. Turbulence due to injecting pressurized bearing gas against a large spinning sample, sample holder, or outer housing may cause the spinning component to wobble (or be unstable) at high speeds. Furthermore, maintaining the position of the sample or inner sample holder in a DOR system is difficult to do using air/gas bearings.